1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to an air riding seal between a rotor and a stator in a turbine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Air riding seals are designed to provide non-contacting sealing between a rotating part and a stationary part, usually within a gas turbine engine. This is done by providing a high pressure supply of fluid to an annular piston that is free to slide axially. The fluid flow is routed to the face between the rotating static components via an orifice creating an annulus of high pressure that keeps the seal piston from contacting the face of the rotating body. The high pressure fluid is allowed to leak out of the cavity radially inward and outward in small quantities in order to regulate a gap between the rotating and the static components. These seals are highly effective at limiting leakage when compared to other more traditional alternatives such as a labyrinth seal or a brush seal.
Because air riding seals rely on the high pressure supply fluid to operate, secondary seals are required to ensure minimal leakage out of the high pressure cavity. The secondary seals need to be able to accommodate the axial sliding that occurs as the piston “follows” the axial motion of the rotor during operation. In common practice, these seals are piston type C-seals or ring seals. These secondary seals provide decent sealing but they still allow some leakage, thus lowering the effectiveness of the entire seal package. An additional feature, such as a spring, is also commonly used to pull the piston off of the rotor face during transient shutdown and startup conditions so as to minimize static to rotating rubbing.